JP2016012521A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect, in a fuel cell system including a combustion catalyst, reduction in catalytic reaction of the combustion catalyst.SOLUTION: A fuel cell system includes: a fuel cell 34 for generating power using fuel and an oxidant gas; a combustion unit 36 for combusting, using the oxidant gas, an anode off-gas lead after being discharged from the fuel cell 34; a combustion catalyst 28 for combusting, using catalytic reaction, a combustible component included in a combustion gas discharged from the combustion unit 36; an oxygen ratio change unit (controller 15) for increasing a flow rate of a combustible component having not been combusted to be led from the combustion unit 36 to the combustion catalyst 28, by changing an oxygen ratio λ obtained by dividing an oxygen flow rate led to the combustion unit 36 by an ideal oxygen flow rate necessary for making a combustible component led to the combustion unit 36 be completely combusted; and a determination unit (controller 15) for determining whether or not the catalytic reaction of the combustion catalyst 28 has reduced on the basis of a temperature on the combustion catalyst 28, when the oxygen ratio λ has been changed by the oxygen ratio change unit.

Description

  The present invention relates to a fuel cell system.

  As one type of fuel cell system, one shown in Patent Document 1 is known. As shown in FIG. 1 of Patent Document 1, such a fuel cell system includes a reforming unit (reforming catalyst 3) that generates reformed gas containing hydrogen from reformed water and a reforming raw material. And a fuel cell (fuel cell stack 1) that generates electric power using the reformed gas and air, and a combustion catalyst (9) that combusts the anode off-gas and cathode off-gas discharged from the fuel cell by catalytic reaction. .

  In the fuel cell system disclosed in Patent Document 1, the flow rate of the anode offgas flowing into the combustion catalyst and the component concentration of the anode offgas are detected, and the combustion catalyst is set so that the temperature of the combustion catalyst becomes an allowable temperature based on the detection result. The amount of air supplied to is controlled.

JP 2002-316801 A

  If the catalytic reaction in the combustion catalyst decreases due to foreign matters adhering to the surface of the combustion catalyst, a part of the combustible component or the combustible component introduced into the combustion catalyst is not completely burned in the combustion catalyst. The whole is discharged as it is outside the fuel cell system. The fuel cell system disclosed in Patent Document 1 does not disclose any technique for detecting a decrease in the catalytic reaction of the combustion catalyst.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to detect a decrease in the catalytic reaction of a combustion catalyst in a fuel cell system provided with the combustion catalyst.

  The invention of the fuel cell system according to claim 1, which has been made to solve the above problems, includes a reforming unit that generates fuel from reforming water and a reforming raw material, and the reforming unit includes the reforming unit. A fuel supply unit for supplying raw materials, a fuel cell that generates electricity with the fuel and an oxidant gas, a combustion unit for burning an anode off-gas containing combustible components exhausted from the fuel cell with an oxidant gas, and A combustion catalyst that introduces a combustion gas containing the unburned combustible component exhausted from the combustion section and burns the combustible component contained in the combustion gas by a catalytic reaction, and a temperature at which a temperature related to the combustion catalyst is detected. The oxygen ratio obtained by dividing the oxygen flow rate introduced into the detection unit and the combustion unit by the ideal oxygen flow rate necessary for complete combustion of the combustible component introduced into the fuel unit is changed, and the oxygen flow rate is changed. Ratio changed When the oxygen ratio is changed by the oxygen ratio changing unit that increases the flow rate of the unburned combustible component introduced from the combustion unit to the combustion catalyst, and the oxygen ratio changing unit, And a determination unit that determines whether or not the catalytic reaction of the combustion catalyst is reduced based on the temperature related to the combustion catalyst detected by the temperature detection unit.

  When the flow rate of unburned combustible components introduced into the combustion catalyst is increased, if the catalytic reaction of the combustion catalyst is not reduced, the combustible components are completely burned by the combustion catalyst and the flow rate of the combustible components is increased. The temperature of the combustion catalyst rises compared to before it is done. On the other hand, when the flow rate of the unburned combustible component introduced into the combustion catalyst is increased, the temperature of the combustion catalyst does not rise compared to before the flow rate of the combustible component is increased, or the combustion catalyst When the temperature of the combustion chamber hardly increases, the combustible component is not combusted by the combustion catalyst or the combustible component is incompletely combusted by the combustion catalyst due to a decrease in the catalytic reaction of the combustion catalyst. It is. Using such a principle, the determination unit relates to the combustion catalyst detected by the temperature detection unit when the flow rate of unburned combustible components introduced from the combustion unit to the combustion catalyst is increased by the oxygen ratio changing unit. Based on the temperature, it can be determined whether the catalytic reaction of the combustion catalyst is reduced. Therefore, in the fuel cell system provided with the combustion catalyst, it is possible to detect a decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 2 is the invention according to claim 1, wherein the oxygen ratio changing unit is configured to set the oxygen ratio from an incomplete combustion start oxygen ratio at which incomplete combustion of the combustible component occurs in the combustion unit. To lower oxygen ratio. As a result, incomplete combustion occurs in the combustion part, and combustible components that are not combusted in the combustion part are reliably introduced into the combustion catalyst. For this reason, the fall of the catalytic reaction of a combustion catalyst can be determined reliably.

  The invention according to claim 3 is the invention according to claim 2, wherein the oxygen ratio changing unit supplies the fuel supplied by the fuel supply unit compared to before the oxygen ratio is reduced to the determined constant oxygen ratio. The oxygen ratio is decreased to the determined constant oxygen ratio. Thereby, the flow volume of the combustible component supplied to the combustion part can be increased reliably, and the oxygen ratio of the gas introduced into the combustion part can be reduced to the determination constant oxygen ratio. For this reason, incomplete combustion can be reliably generated in the combustion section, and combustible components that are not burned in the combustion section can be reliably introduced into the combustion catalyst. Therefore, it is possible to reliably determine the decrease in the catalytic reaction of the combustion catalyst. In addition, when reducing the oxygen ratio, the supply amount of fuel is increased rather than decreasing the supply of oxidant gas, preventing the fuel cell system from shutting down due to insufficient oxygen in the fuel cell. It is possible to determine a decrease in the catalytic reaction of the combustion catalyst while continuing the operation of the fuel cell system.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, a sweep current changing unit that changes a sweep current that is a current swept from the fuel cell, and an oxidation that supplies the oxidant gas to the fuel cell. And the oxygen ratio changing unit controls the sweep current changing unit so that the sweep current is reduced as compared to before reducing the oxygen ratio to the determined constant oxygen ratio. The oxygen ratio is reduced to the determined constant oxygen ratio by controlling the oxidant gas supply unit so that the flow rate of the oxidant gas is decreased by the flow rate of the oxidant gas according to the decrease in the sweep current. Let Thereby, when the sweep current decreases, the flow rate of hydrogen consumed in the fuel cell decreases, and the flow rate of hydrogen introduced into the combustion section increases. In addition, although the flow rate of oxygen consumed in the fuel cell is reduced by reducing the sweep current, the flow rate of the oxidant gas is reduced by an amount corresponding to the flow rate of the oxidant gas in accordance with the decrease in the sweep current, and combustion is thereby performed. The flow rate of oxygen supplied to the section does not increase. Thereby, the flow rate of the combustible component supplied to the combustion unit can be reliably increased without increasing the flow rate of oxygen supplied to the combustion unit, and the oxygen ratio of the gas introduced into the combustion unit can be determined. Ratio can be reduced. For this reason, incomplete combustion can be reliably generated in the combustion section, and combustible components that are not burned in the combustion section can be reliably introduced into the combustion catalyst. Therefore, it is possible to reliably determine the decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 5 is the invention according to claim 3, wherein the oxygen is based on a sweep current that is a current swept from the fuel cell and a flow rate of the oxidant gas supplied to the fuel cell. A command fuel flow rate calculation unit that calculates a commanded fuel flow rate that is a flow rate of the fuel at which the ratio decreases to the determined constant oxygen ratio, and the oxygen ratio change unit has a flow rate of the fuel supplied by the fuel supply unit The fuel supply unit is controlled to achieve the indicated fuel flow rate. Thus, the command fuel flow rate at which the oxygen ratio is reduced to the determination oxygen ratio is calculated, and the fuel supply unit is controlled so that the flow rate of the fuel supplied by the fuel supply unit becomes the command fuel flow rate. Thereby, the oxygen ratio of the gas supplied to the combustion unit can be accurately and more reliably set to the determination oxygen ratio. For this reason, incomplete combustion can be reliably generated in the combustion section, and combustible components that are not burned in the combustion section can be more reliably introduced into the combustion catalyst. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 6 is swept from the fuel cell in which the oxygen ratio is reduced to the determined constant oxygen ratio based on the flow rate of the fuel supplied by the fuel supply unit in the invention according to claim 4. Based on the flow rate of the fuel supplied by the fuel supply unit and the command current calculated by the command current calculation unit, the oxygen ratio is determined by the determined constant oxygen. An indicator oxidant gas flow rate calculation unit that calculates an indicator oxidant gas flow rate that is a flow rate of the oxidant gas that decreases to a ratio, and the oxygen ratio change unit sweeps the sweep current from the fuel cell. The sweep current changing unit to control the oxidant gas supply unit so that the flow rate of the oxidant gas supplied to the fuel cell becomes the indicated oxidant gas flow rate. To. In this way, the command current at which the oxygen ratio becomes the determination oxygen ratio is calculated, the sweep current swept from the fuel cell is changed to the command current, and the command oxidant gas flow rate at which the oxygen ratio becomes the determination oxygen ratio is calculated. Thus, the flow rate of the oxidant gas supplied by the oxidant gas supply unit is changed to the indicated oxidant gas flow rate. Thereby, the oxygen ratio of the gas supplied to the combustion unit can be accurately and more reliably set to the determination oxygen ratio. For this reason, incomplete combustion can be reliably generated in the combustion section, and combustible components that are not burned in the combustion section can be more reliably introduced into the combustion catalyst. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 7 is the invention according to claim 5, further comprising a reforming unit temperature detecting unit that detects a temperature of the reforming unit, wherein the indicated fuel flow rate calculating unit is configured to detect the reforming unit temperature. The indicated fuel flow rate is calculated based on the temperature of the reforming section detected by the section. Thus, the command fuel flow rate calculation unit can calculate the composition of the fuel generated by the reforming unit based on the temperature of the reforming unit. The command fuel flow rate calculation unit calculates the command fuel flow rate based on the calculated fuel composition. Thus, the indicated fuel flow rate is calculated such that the oxygen ratio of the gas supplied to the combustion section becomes the determination oxygen ratio with higher accuracy than in the case where it is not based on the fuel composition. For this reason, the oxygen ratio of the gas supplied to the combustion section can be more reliably set to the determination oxygen ratio, incomplete combustion can be more reliably generated in the combustion section, and combustible that has not been burned in the combustion section. The components can be more reliably introduced into the combustion catalyst. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 8 is the invention according to claim 6, further comprising a reforming unit temperature detection unit that detects a temperature of the reforming unit, and the command current calculation unit is controlled by the reforming unit temperature detection unit. The indicator current is calculated based on the detected temperature of the reforming unit. Thereby, the composition of the fuel produced | generated by the reforming part is computable based on the temperature of a reforming part. The command current calculation unit calculates the command current based on the calculated fuel composition. Thus, the indicated fuel flow rate is calculated such that the oxygen ratio of the gas supplied to the combustion section becomes the determination oxygen ratio with higher accuracy than in the case where it is not based on the fuel composition. For this reason, the oxygen ratio of the gas supplied to the combustion section can be more reliably set to the determination oxygen ratio, incomplete combustion can be more reliably generated in the combustion section, and combustible that has not been burned in the combustion section. The components can be more reliably introduced into the combustion catalyst. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the temperature detection unit detects a temperature of exhaust gas exhausted from the combustion catalyst or a temperature of the combustion catalyst, and performs the determination. And when the oxygen ratio is changed by the oxygen ratio changing unit and the temperature detected by the temperature detecting unit is lower than a determination temperature, the unit determines that the catalytic reaction of the combustion catalyst has decreased. . As a result, the flow rate of unburned combustible components introduced into the combustion catalyst is increased with the change in the oxygen ratio, and the temperature of the exhaust gas detected by the temperature detection unit or the temperature of the pre-combustion catalyst does not reach the determination temperature. In this case, it is determined that the catalytic reaction is decreasing. In this way, it is possible to determine a decrease in the catalytic reaction of the combustion catalyst without providing a plurality of temperature detection units. For this reason, the increase in the manufacturing cost of a fuel cell system can be suppressed.

  The invention according to claim 10 is the invention according to any one of claims 1 to 8, wherein the temperature detector detects a temperature of exhaust gas exhausted from the combustion catalyst or a temperature of the combustion catalyst. A detection unit and a second temperature detection unit for detecting the temperature of the combustion gas introduced into the combustion catalyst, and the determination unit is configured when the oxygen ratio is changed by the oxygen ratio changing unit. When the temperature difference obtained by subtracting the temperature detected by the second temperature detector from the temperature detected by the first temperature detector is less than a specified temperature difference, the catalytic reaction of the combustion catalyst is reduced. It is determined that In this way, whether or not the catalytic reaction of the combustion catalyst is reduced by the temperature difference of the exhaust gas exhausted from the combustion catalyst or the temperature difference obtained by subtracting the temperature of the combustion gas introduced into the combustion catalyst from the temperature of the combustion catalyst. Determined. As a result, it is possible to reliably detect an increase in the temperature of the combustion catalyst accompanying an increase in the flow rate of the combustible component introduced into the combustion catalyst, regardless of the temperature of the combustion gas. For this reason, it can be determined with higher accuracy whether the catalytic reaction of the combustion catalyst is reduced.

It is a schematic diagram showing an outline of one embodiment (first embodiment) of a fuel cell system according to the present invention. It is a graph showing the relationship between the oxygen ratio λ of the mixed gas introduced into the combustion section and the temperature T2 of the exhaust gas exhausted from the combustion catalyst. It is explanatory drawing which showed the outline | summary of the method of calculating oxygen ratio (lambda) of the mixed gas introduce | transduced into a combustion part. It is the mapping data which showed the relationship between the temperature of a reforming part, and a reformed gas composition. 3 is a flowchart of a “first catalyst reaction decrease determination process” executed by the control device shown in FIG. 1. 3 is a flowchart of a “second catalyst reaction decrease determination process” executed by the control device shown in FIG. 1. It is a schematic diagram which shows the outline | summary of the fuel cell system of 2nd embodiment.

  Hereinafter, an embodiment of the fuel cell system 100 according to the present invention will be described. As shown in FIG. 1, the fuel cell system 100 includes a power generation unit 10 and a hot water storage tank 21. The power generation unit 10 includes a housing 10a, a fuel cell module 11, a heat exchanger 12, an inverter device 13, a water tank 14, a control device 15, and a notification unit 17.

  The fuel cell module 11 includes a casing 31, an evaporation unit 32, a reforming unit 33, and a fuel cell 34. The casing 31 is formed in a box shape with a heat insulating material. The evaporation unit 32 is heated by combustion gas burned by the combustion unit 36 described later, evaporates the supplied reforming water to generate steam, and preheats the supplied reforming raw material. . The evaporation section 32 mixes the steam generated in this way and the preheated reforming raw material and supplies the mixture to the reforming section 33.

  One end of a reforming material supply pipe 11a is connected to the evaporation section 32. A supply source Gs is connected to the other end of the reforming material supply pipe 11a. The supply source Gs supplies a raw material for reforming. As reforming raw materials, there are gas fuels for reforming such as natural gas and LP gas, and liquid fuels for reforming such as kerosene, gasoline and methanol. A fuel cell system 100 according to this embodiment will be described with respect to an embodiment using natural gas as a reforming raw material.

  The reforming material supply pipe 11a is provided with a shut-off valve 11a1, a desulfurizer 11a2, a reforming material flow rate sensor 11a3, a buffer tank 11a4, a material pump 11a5, and a check valve 11a6 in order from the upstream. The shut-off valve 11a1 is a valve (double valve) that shuts off the reforming material supply pipe 11a in a freely openable / closable state according to a command from the control device 15. The desulfurizer 11a2 removes a sulfur content (for example, a sulfur compound) in the reforming raw material. The reforming material flow rate sensor 11 a 3 detects the flow rate of the reforming material supplied to the evaporation unit 32, that is, the flow rate per unit time, and transmits the detection result to the control device 15. The buffer tank 11a4 suppresses a decrease in accuracy of the reforming raw material flow rate sensor 11a3 and a deviation from the true value due to the pulsation of the raw material pump 11a5.

  The raw material pump 11 a 5 is a supply device that supplies a reformed raw material (fuel) to the fuel cell 34 by supplying the raw material for reforming to the evaporation section 32. The fuel supply amount (supply flow rate (flow rate per unit time)) is adjusted. The check valve 11a6 is disposed between the raw material pump 11a5 and the fuel cell module 11 (evaporating part 32), and allows the flow from the raw material pump 11a5 to the fuel cell module 11, but the flow in the opposite direction is allowed. It is forbidden.

  One end of a water supply pipe 11b is connected to the evaporation section 32. The other end of the water supply pipe 11b is connected to the water tank. The water supply pipe 11b is provided with a reforming water pump 11b1. With such a configuration, the reformed water is supplied from the water tank 14 to the evaporation unit 32.

  One end of a cathode air supply pipe 11 c is connected to the fuel cell 34. A cathode air blower 11c1 is connected to the other end of the cathode air supply pipe 11c. With such a configuration, cathode air is supplied to the fuel cell 34. A cathode air flow sensor 11c2 for detecting the flow rate of cathode air supplied to the fuel cell 34 is provided on the downstream side of the cathode air blower 11c1 of the cathode air supply pipe 11c.

The reforming unit 33 is heated by the combustion gas burned by the combustion unit 36 described later and supplied with heat necessary for the steam reforming reaction, so that the source gas (reforming raw material) supplied from the evaporation unit 32 is supplied. , Water vapor) to generate and derive the reformed gas. The reforming unit 33 is filled with a catalyst (for example, Ru or Ni-based catalyst), and the raw material gas reacts with the catalyst and is reformed to generate a gas containing hydrogen gas and carbon monoxide. (So-called steam reforming reaction). That is, in the reforming part 33, the reactions shown in the following chemical formulas 1 and 2 occur.
(Chemical Formula 1) CH ₄ + H ₂ O → CO + 3H ₂
(Chemical Formula 2) H ₂ O + CO⇔H ₂ + CO ₂
The reformed gas thus generated contains hydrogen, carbon monoxide, carbon dioxide, steam, unreformed natural gas (methane gas), and reformed water (steam) that has not been used for reforming. As described above, the reforming unit 33 generates reformed gas (fuel) from the reforming raw material and the reformed water and supplies the reformed gas (fuel) to the fuel cell 34. The steam reforming reaction is an endothermic reaction.

  The reforming unit 33 is provided with a reforming unit temperature sensor 33a that detects the temperature T1 (catalyst temperature) of the reforming unit 33. The detection result (output signal) of the reforming unit temperature sensor 33 a is transmitted to the control device 15.

  The fuel cell 34 generates power using the reformed gas (fuel) generated by the reforming unit 33 and the cathode air (oxidant gas) supplied by the cathode air blower 11c1. The fuel cell 34 is configured by laminating a fuel electrode, an air electrode (oxidant electrode), and a plurality of cells 34a made of an electrolyte interposed between the two electrodes. The fuel cell 34 of the present embodiment is a solid oxide fuel cell, and uses zirconium oxide, which is a kind of solid oxide, as an electrolyte. Hydrogen, carbon monoxide, methane gas, etc. are supplied to the fuel electrode of the fuel cell 34 as fuel.

In the fuel electrode, the reactions shown in Chemical Formula 3 and Chemical Formula 4 below occur.
(Chemical formula 3)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻
(Chemical formula 4)
CO + O ²⁻ → CO ₂ + 2e ⁻

In the air electrode, the reaction shown in Chemical Formula 5 below occurs.
(Chemical formula 5)
1 / 2O ₂ + 2e ⁻ → O ₂ ⁻
That is, oxide ions (O ²⁻ ) generated at the air electrode permeate the electrolyte and react with hydrogen at the fuel electrode to generate electrical energy.

  The operating temperature of the fuel cell 34 is about 400 to 1000 ° C. Not only hydrogen but also natural gas and coal gas can be used directly as fuel.

  On the fuel electrode side of the cell 34a, a fuel flow path 34b through which the reformed gas as the fuel flows is formed. An air flow path 34c through which air (cathode air) that is an oxidant gas flows is formed on the air electrode side of the cell 34a.

  The fuel cell 34 is provided on the manifold 35. The reformed gas from the reforming unit 33 is supplied to the manifold 35 via the reformed gas supply pipe 38. The lower end (one end) of the fuel flow path 34b is connected to the fuel outlet of the manifold 35, and the reformed gas led out from the fuel outlet is introduced from the lower end and led out from the upper end. . The cathode air sent out by the cathode air blower 11c1 is supplied via the cathode air supply pipe 11c, introduced from the lower end of the air flow path 34c, and led out from the upper end.

  The combustion unit 36 is provided between the fuel cell 34, the evaporation unit 32, and the reforming unit 33. The combustion unit 36 burns anode off-gas (fuel off-gas) containing combustible components exhausted from the fuel cell 34 with cathode off-gas (oxidant off-gas) exhausted from the fuel cell 34, and uses combustion gas generated after combustion. The evaporation unit 32 and the reforming unit 33 are heated.

  In the combustion unit 36, the anode off gas is burned and a flame 37 is generated. The combustion unit 36 is provided with a pair of ignition heaters 36a1 and 36a2 for igniting the anode off gas.

  The heat exchanger 12 is a device that is supplied with exhaust gas exhausted from the fuel cell module 11 and supplied with hot water from the hot water storage tank 21 to exchange heat between the exhaust gas and hot water. The hot water storage tank 21 stores hot water, and is connected to a hot water circulation line 22 through which the hot water circulates (circulates in the direction of the arrow in FIG. 1). On the hot water circulation line 22, a circulation pump 22 a and a heat exchanger 12 are arranged in order from the lower end to the upper end of the hot water tank 21. The heat exchanger 12 is connected to a condensed water supply pipe 12 a connected to the water tank 14.

  In the heat exchanger 12, the exhaust gas from the fuel cell module 11 is introduced into the heat exchanger 12 through the exhaust gas introducing portion 12b, and is cooled by exchanging heat with the hot water stored in the exhaust gas. The water vapor contained in the water is condensed to produce condensed water. The exhaust gas after heat exchange passes through the exhaust pipe 12c, passes through the first exhaust port 10b provided in the housing 10a, and is discharged to the outside of the housing 10a. Moreover, the condensed condensed water is supplied to the water tank 14 through the condensed water supply pipe 12a. The water tank 14 purifies the condensed water with ion exchange resin.

  The heat exchanger 12, the hot water tank 21, and the hot water circulation line 22 described above constitute an exhaust heat recovery system 20. The exhaust heat recovery system 20 recovers and stores the exhaust heat of the fuel cell module 11 in hot water storage.

  A combustion catalyst 28 is provided at a portion where the inlet of the exhaust gas inlet 12 b of the heat exchanger 12 is connected to the casing 31, that is, at the outlet 31 a of the casing 31. Combustion gas exhausted from the combustion unit 36 is introduced into the combustion catalyst 28. The combustion catalyst 28 burns unburned combustible components (for example, hydrogen, methane gas, carbon monoxide, etc.) by a catalytic reaction in the combustion section 36 included in the combustion gas. The combustion catalyst 28 includes a catalyst in which a precious metal such as platinum or palladium is supported on a single ceramic body. The combustion catalyst 28 burns combustible components such as hydrogen, methane gas, and carbon monoxide not by flame combustion but by a catalytic reaction. The combustion catalyst 28 has a high combustion speed and high combustion efficiency, so that the emission of unburned gas can be suppressed. .

  The combustion catalyst 28 is provided with a combustion catalyst heater 28a for heating the combustion catalyst to the activation temperature of the catalyst and combusting combustible components. The combustion catalyst heater 28a is heated by an instruction from the control device 15, and is used to raise the combustion catalyst 28 to an activation temperature before the system is started. A temperature sensor 28b (temperature detection unit) for detecting the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 is provided immediately downstream of the combustion catalyst 28. The detection result (output signal) of the temperature sensor 28 b is transmitted to the control device 15.

  The inverter device 13 sweeps the current generated by the fuel cell 34. This current is hereinafter referred to as a sweep current. The inverter device 13 converts the swept current, which is a swept DC current, into an AC current, and outputs the AC power to the power supply line 16b connected to the AC system power supply 16a and the external power load 16c (for example, an electrical appliance). To do. The inverter device 13 can detect the current value of the sweep current and can increase or decrease the sweep current amount. An alternating current from the system power supply 16a is input to the inverter device 13 through the power supply line 16b. The inverter device 13 converts the input alternating current into a predetermined direct current and outputs the converted direct current to an auxiliary machine (each pump, blower, etc.) or the control device 15.

  The control device 15 performs overall control of the fuel cell system 100. The control device 15 controls the operation of the fuel cell system 100 by driving an auxiliary machine. The control device 15 feedback-controls the flow rate of the reforming material supplied to the evaporation unit 32 by the material pump 11a5 based on the flow rate of the reforming material to the evaporation unit 32 detected by the reforming material flow rate sensor 11a3. To do. Further, the control device 15 feedback-controls the flow rate of the cathode air supplied from the cathode air blower 11c1 to the fuel cell 34 based on the flow rate of the cathode air to the fuel cell 34 detected by the cathode air flow rate sensor 11c2. The control device 15 adjusts the amount of current supplied to a motor (not shown) for driving the raw material pump 11a5 and a motor (not shown) for driving the cathode air blower 11c1 by linear current control. Here, the linear current control includes PWM control for changing the voltage duty ratio for driving the raw material pump 11a5 and changing the effective current.

  The control device 15 adjusts the flow rate of the reforming raw material supplied to the evaporation unit 32 by the raw material pump 11a5, adjusts the flow rate of the reforming water supplied to the evaporation unit 32 by the reforming water pump 11b1, By adjusting the flow rate of cathode air supplied to the fuel cell 34 by the cathode air blower 11c1, the generated power generated by the fuel cell 34 is adjusted and the amount of heat generated in the combustion unit 36 is adjusted to evaporate. The amount of heat supplied to the section 32 and the reforming section is adjusted.

(Explanation of catalytic reaction decrease judgment method)
A method for determining whether or not the catalytic reaction of the combustion catalyst 28 has decreased will be described below using the graph shown in FIG. FIG. 2 is a graph showing the relationship between the oxygen ratio λ of the mixed gas, which is a mixture of the anode off-gas and the cathode off-gas introduced into the combustion unit 36, and the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28.
In FIG. 2, the oxygen ratio λ is a value shown in the following formula (1).
λ = A / B (1)
λ = oxygen ratio A = oxygen flow rate actually introduced into the combustor 36 B = ideal oxygen flow rate necessary for complete combustion of combustible components contained in the anode off-gas

  When the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 becomes lower than the incomplete combustion start oxygen ratio λ 0 (for example, 1.2) at which incomplete combustion of the mixed gas is started in the combustion unit 36, the combustion unit 36. The anode off gas burns incompletely. Then, the flow rate of the combustible component contained in the combustion gas exhausted from the combustion unit 36 and introduced into the combustion catalyst 28 increases. Then, since the combustible component contained in the combustion gas introduced into the combustion catalyst 28 burns in the combustion catalyst 28, the oxygen ratio λ of the mixed gas introduced into the combustion section 36 is not as shown in 1 of FIG. The temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 increases as compared with the case where the complete combustion start oxygen ratio λ0 is higher.

  On the other hand, when the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is higher than the incomplete combustion start oxygen ratio λ0, the anode off-gas almost burns in the combustion unit 36. As a result, the flow rate of the combustible component introduced into the combustion catalyst 28 is reduced compared with the case where the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is lower than the incomplete combustion start oxygen ratio λ0, and the combustion catalyst 28 combusts. The amount of heat generated due to the combustion of the components decreases, and the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 also decreases.

  2 is used to reduce the oxygen ratio λ of the mixed gas introduced into the combustion section 36 to a determination oxygen ratio λa lower than the incomplete combustion start oxygen ratio λ0. The flow rate of the combustible component contained in the combustion gas introduced into 28 is increased. Then, it is determined whether or not the combustion reaction of the combustion catalyst 28 is decreasing depending on whether or not the temperature of the combustion catalyst 28 rises above the determination temperature T2a. That is, when the catalytic reaction in the combustion catalyst 28 is reduced, even if the flow rate of the combustible component contained in the combustion gas introduced into the combustion catalyst 28 is increased, the combustible component is reacted in the combustion catalyst 28. Therefore, the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 does not increase as compared with the case where the catalytic reaction of the combustion catalyst 28 does not decrease. Using this principle, even if the oxygen ratio λ of the mixed gas introduced into the combustion section 36 is lowered to the determination oxygen ratio λa lower than the incomplete combustion start oxygen ratio λ0, the temperature of the combustion catalyst 28 becomes equal to or higher than the determination temperature T2a. If it has not increased, it is determined that the catalytic reaction of the combustion catalyst 28 has decreased.

(Calculation method of oxygen ratio λ)
Next, a method for calculating the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 will be sequentially described below with reference to FIGS. 3 and 4.
(1) The flow rate of the reformed gas flowing out from the reforming unit 33 is calculated based on the flow rate of the reforming material detected by the reforming material flow rate sensor 11a3.

(2) Based on the temperature of the reforming unit 33 detected by the reforming unit temperature sensor 33a, the reformed gas composition is calculated with reference to the mapping data shown in FIG. As shown in FIG. 4, the proportion of methane (CH ₄ ) contained in the reformed gas decreases as the temperature of the reforming unit 33 increases. Further, as the temperature of the reforming section 33 increases, the proportion of hydrogen (H ₂ ) contained in the reformed gas increases. Further, as the temperature of the reforming section 33 increases, the proportion of carbon monoxide (CO) contained in the reformed gas increases, but does not increase more than the proportion of hydrogen.

(3) Based on the flow rate of the reformed gas calculated in (1) and the composition of the reformed gas calculated in (2), each of the reformed gases supplied from the reforming unit 33 to the fuel cell 34 The flow rate of the combustible component is calculated.
(4) The flow rate of hydrogen consumed in the fuel cell 34 is calculated based on the sweep current swept from the fuel cell 34.

(5) Based on the flow rate of each combustible component of the reformed gas supplied to the fuel cell 34 calculated in (3) and the flow rate of hydrogen consumed in the fuel cell 34 calculated in (4), the fuel The flow rate of each combustible component of the anode off gas supplied from the battery 34 to the combustion unit 36 is calculated. That is, the flow rate of hydrogen contained in the anode off gas is calculated by subtracting the flow rate of hydrogen consumed in the fuel cell 34 from the flow rate of hydrogen contained in the reformed gas. Then, the flow rate of each combustible component excluding hydrogen among the combustible components of the reformed gas is calculated as the flow rate of each combustible component excluding hydrogen among the combustible components of the anode off gas.

(6) Based on the flow rate of each combustible component of the anode off gas calculated in (5), the ideal amount of oxygen necessary to completely burn the anode off gas supplied to the combustion unit 36 is calculated.

(7) The flow rate of oxygen consumed in the fuel cell 34 is calculated based on the sweep current swept from the fuel cell 34.
(8) Based on the flow rate of the cathode air detected by the cathode air flow rate sensor 11c2 and the flow rate of oxygen consumed in the fuel cell 34 calculated in (7), the fuel cell 34 supplies the combustion unit 36 with the flow rate. The flow rate of oxygen contained in the cathode off gas is calculated. That is, the flow rate of oxygen consumed in the fuel cell 34 is subtracted from the flow rate of oxygen contained in the cathode air to calculate the flow rate of oxygen contained in the cathode off gas.

(9) By dividing the flow rate of oxygen contained in the cathode offgas calculated in (8) by the ideal amount of oxygen necessary for complete combustion of the anode offgas calculated in (6), the combustion unit 36 The oxygen ratio λ of the mixed gas introduced into is calculated.
Below, the specific method of determining the fall of a catalytic reaction with the combustion catalyst 28 is demonstrated.

(First catalytic reaction decrease judgment process)
The “first catalyst reaction decrease determination process” will be described below using the flowchart shown in FIG. The “first catalyst reaction decrease determination process” is a process for determining the reforming raw material supplied to the evaporation section 32 while maintaining the sweep current swept from the fuel cell 34 and the flow rate of the cathode air supplied to the fuel cell 34. By increasing the flow rate, that is, by increasing the flow rate of the reformed gas supplied to the fuel cell 34, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 is set as the determination oxygen ratio λa, and the catalyst of the combustion catalyst 28 This is a method for determining whether or not the reaction has decreased. When the fuel cell system is activated, the control device 15 advances the program to step S11.

  In step S11, the control device 15 starts power generation in the fuel cell 34 by controlling the raw material pump 11a5, the cathode air blower 11c1, and the reforming water pump 11b1. When step S11 ends, the control device 15 advances the program to step S12.

  In step S12, the control device 15 (instructed fuel flow rate calculation unit) refers to the mapping data shown in FIG. 4 based on the temperature of the reforming unit 33 detected by the reforming unit temperature sensor 33a, thereby reforming. Calculation of the composition of the reformed gas supplied from the unit 33 to the fuel cell 34 is started (2 in FIG. 3). When step S12 ends, the control device 15 advances the program to S13.

  In step S13, the control device 15 (instructed fuel flow rate calculation unit) starts calculating the flow rate of hydrogen consumed in the fuel cell 34 based on the sweep current being swept from the fuel cell 34 by the inverter device 13 ( 4) of FIG. When step S13 ends, the control device 15 advances the program to S14.

  In step S <b> 14, the control device 15 (indicated fuel flow rate calculation unit) starts calculating the flow rate of oxygen consumed in the fuel cell 34 based on the sweep current being swept from the fuel cell 34 by the inverter device 13 ( 7) in FIG. Next, the control device 15 (instructed fuel flow rate calculation unit) determines from the fuel cell 34 to the combustion unit 36 based on the cathode air flow rate detected by the cathode air flow rate sensor 11c2 and the oxygen flow rate consumed in the fuel cell 34. The calculation of the flow rate of oxygen contained in the cathode off gas supplied to is started (8 in FIG. 3). When step S14 ends, the control device 15 advances the program to step S21.

  In step S21, the control device 15 starts counting of the timer TM. When step S21 ends, the control device 15 advances the program to step S22.

  In step S22, when it is determined that the timer TM has passed a specified time TMa (for example, 1 day) (step S22: YES), the control device 15 advances the program to S23. On the other hand, when it is determined that the timer TM has not passed the specified time TMa (step S22: NO), the control device 15 repeats the process of step S22.

  In step S23, the control device 15 (indicated fuel flow rate calculation unit) uses the above-described method described with reference to FIG. 3 to determine the composition of the reformed gas that has been calculated in step S12 and the fuel cell that has been calculated in step S13. Based on the hydrogen consumption flow rate at 34 and the flow rate of oxygen contained in the cathode off-gas calculated at step S14, the indicated raw material flow rate Fa that provides the determination oxygen ratio λa is calculated. The determination oxygen ratio λa is the oxygen ratio of the mixed gas introduced into the combustion unit 36 when determining whether the catalytic reaction of the combustion catalyst 28 is decreasing. The determination oxygen ratio λa is exhausted from the combustion catalyst 28 when the oxygen ratio λ of the mixed gas introduced into the combustion section 36 is set to the determination oxygen ratio λa when the catalytic reaction of the combustion catalyst 28 has not decreased. The value is such that the temperature T2 of the exhaust gas to be made becomes the determination temperature T2a. The determination oxygen ratio λa is preferably 1 or more. When the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to a determination oxygen ratio λa of less than 1, soot is generated due to incomplete combustion of combustible components in the combustion unit 36, This is because the flow path downstream of the combustion unit 36 may be blocked. In addition, the indicated raw material flow rate Fa is supplied by the raw material pump 11a5 that has the determination oxygen ratio λa while the sweep current swept from the fuel cell 34 and the flow rate of the cathode air supplied to the fuel cell 34 are maintained. This is the flow rate of the raw material for reforming. When step S23 ends, the control device 15 advances the program to step S24.

  In step S24, the controller 15 (oxygen ratio changing unit) determines the flow rate of the reforming material supplied by the material pump 11a5 based on the flow rate of the reforming material detected by the reforming material flow rate sensor 11a3. The raw material pump 11a5 is feedback-controlled so that the indicated raw material flow rate Fa calculated in S23 is obtained. By this control, the flow rate of the reforming raw material supplied by the raw material pump 11a5 is increased as compared with that before step S24 is executed. The control device 15 (oxygen ratio changing unit) is configured so that the flow rate of the reforming raw material supplied by the raw material pump 11a5 is gradually increased to the indicated raw material flow rate Fa after a predetermined time (for example, several tens of seconds). The raw material pump 11a5 is controlled. As a result, the sudden increase in the flow rate of the reforming raw material prevents the occurrence of partial blow-out in which a part of the flame disappears or complete blow-out in which all the flame disappears in the combustion section 36. By the process of step S24, the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 gradually becomes the determination oxygen ratio λa. In addition, the control device 15 increases the flow rate of the reforming water supplied to the evaporation unit 32 by the reforming water pump 11b1 by a predetermined flow rate compared to before the process of step S24 is started. As a result, the occurrence of coking in the reforming unit 33 accompanying the increase in the flow rate of the reforming material supplied to the evaporation unit 32 is prevented. When step S24 ends, the control device 15 advances the program to step S25.

  In step S25, when the control device 15 (determination unit) determines that the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 detected by the temperature sensor 28b is lower than the determination temperature T2a (step S25: YES), the program proceeds to step S41. On the other hand, when the control device 15 (determination unit) determines that the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 detected by the temperature sensor 28b is equal to or higher than the determination temperature T2a (step S25: NO). ), The program proceeds to step S31. In the case where the catalytic reaction of the combustion catalyst 28 has not decreased, when the oxygen ratio λ of the mixed gas introduced into the combustion section 36 is set to the determination oxygen ratio λa, the combustion is performed as shown by the solid line in FIG. The temperature T2 of the exhaust gas exhausted from the catalyst 28 becomes equal to or higher than the determination temperature T2a, and NO is determined in step S25. On the other hand, when the catalytic reaction of the combustion catalyst 28 is reduced, even if the oxygen ratio λ of the mixed gas introduced into the combustion section 36 is set to the determination oxygen ratio λa, as shown by the broken line in FIG. The temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 becomes lower than the determination temperature T2a, and YES is determined in step S25.

  In step S31, the control device 15 resets the timer TM and advances the program to step S21.

  In step S41, if the control device 15 (determination unit) determines that the second specified time TMb (for example, several seconds to several tens of seconds) has elapsed since it was initially determined to be YES in step S25 (step S41). : YES), the program proceeds to step S42. On the other hand, if the control device 15 (determination unit) determines that the second specified time TMb has not elapsed since it was initially determined to be YES in step S25 (step S41: NO), the program is stepped. Return to S25.

  In step S42, the control device 15 (determination unit) determines that the catalytic reaction in the combustion catalyst 28 has decreased, and advances the program to step S43.

  In step S <b> 43, the control device 15 causes the notification unit 17 to notify an abnormality indicating that the catalytic reaction of the combustion catalyst 28 is decreasing. When step S43 ends, the “first catalytic reaction decrease determination process” ends.

(Effect of this embodiment)
As is clear from the above description, when the flow rate of the unburned combustible component introduced into the combustion catalyst 28 is increased, the combustible component is converted into the combustion catalyst 28 when the catalytic reaction of the combustion catalyst 28 is not lowered. As a result, the temperature of the combustion catalyst 28 rises as compared with before the combustible component flow rate is increased. On the other hand, when the flow rate of the unburned combustible component introduced into the combustion catalyst 28 is increased, but the temperature of the combustion catalyst 28 does not increase compared to before the flow rate of the combustible component is increased, or When the temperature of the combustion catalyst 28 hardly rises, the combustible component is not burned by the combustion catalyst 28 or the combustible component is not burned by the combustion catalyst 28 because the catalytic reaction of the combustion catalyst 28 is lowered. It is in a state of complete combustion. Using such a principle, the control device 15 (determination unit) determines that the temperature of the unburned combustible component introduced from the combustion unit 36 to the combustion catalyst 28 is increased (step S24 in FIG. 5). Based on the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 detected by the sensor 28b, it can be determined whether or not the catalytic reaction of the combustion catalyst 28 has decreased (step S25, step S41, step S42). ). Therefore, in the fuel cell system 100 including the combustion catalyst 28, it is possible to detect a decrease in the catalytic reaction of the combustion catalyst 28.

  Thus, based on the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 detected by the temperature sensor 28b, it is determined whether or not the catalytic reaction of the combustion catalyst 28 has decreased. Thus, the catalytic reaction of the combustion catalyst 28 can be achieved only by providing the temperature sensor 28b without providing the fuel cell system 100 with a sensor for detecting hydrogen and carbon monoxide contained in the exhaust gas exhausted from the combustion catalyst 28. Can be detected. For this reason, the increase in the manufacturing cost of a fuel cell system can be suppressed.

  Further, during the operation of the fuel cell system 100, the flow rate of unburned combustible components introduced from the combustion unit 36 to the combustion catalyst 28 is increased, and combustion is performed based on the temperature of the exhaust gas exhausted from the combustion catalyst 28. It is determined whether or not the catalytic reaction of the catalyst 28 has decreased. For this reason, even if the fuel cell system 100 is not stopped, it can be determined whether or not the catalytic reaction of the combustion catalyst 28 is lowered while the fuel cell system 100 continues to generate power and generate hot water.

  The control device 15 (oxygen ratio changing unit) also sets the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 to be lower than the incomplete combustion start oxygen ratio λ0 at which incomplete combustion of the combustible component occurs in the combustion unit 36. The determination oxygen ratio λa is reduced (step S24 in FIG. 5). As a result, incomplete combustion occurs in the combustion section 36, and combustible components that are not burned in the combustion section 36 can be reliably introduced into the combustion catalyst 28. For this reason, it is possible to reliably determine a decrease in the catalytic reaction of the combustion catalyst 28.

  In addition, the control device 15 (oxygen ratio changing unit) improves the supply supplied by the raw material pump 11a5 (fuel supply unit) compared to before the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to the determination oxygen ratio λa. The flow rate of the raw material (fuel) for quality is increased, and the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to the determination oxygen ratio λa (step S24 in FIG. 5). Thereby, the flow rate of the combustible component supplied to the combustion unit 36 can be reliably increased, and the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 can be set to the determination oxygen ratio λa. For this reason, incomplete combustion can be generated in the combustion part 36, and the combustible component which was not burned in the combustion part 36 can be reliably introduced into the combustion catalyst 28. Therefore, it is possible to reliably determine a decrease in the catalytic reaction of the combustion catalyst 28. Further, when the oxygen ratio λ is lowered, the supply amount of the reforming raw material is increased instead of decreasing the supply amount of the oxidant gas, so that the fuel cell system 100 stops due to oxygen shortage or the like in the fuel cell 34. It is possible to prevent the fuel cell system 100 from continuing to operate, and to determine a decrease in the catalytic reaction of the combustion catalyst 28 while continuing the operation of the fuel cell system 100.

  In addition, the control device 15 (oxygen ratio changing unit) maintains the sweep current swept from the fuel cell 34, and the flow rate of the reforming material (fuel) supplied by the material pump 11a5 (fuel supply unit). To increase the oxygen ratio λ of the mixed gas introduced into the combustion section 36 to the determination oxygen ratio λa (step S24 in FIG. 5), and determine whether the catalytic reaction of the combustion catalyst 28 has decreased. Yes. Thereby, since the sweep current swept from the fuel cell 34 does not decrease, the current supplied to the external power load 16c does not become insufficient.

  Further, the control device 15 (indicated fuel flow rate calculation unit) is introduced into the combustion unit 36 based on the sweep current that is the current swept from the fuel cell 34 and the flow rate of the cathode air supplied to the fuel cell 34. An indicated raw material flow rate Fa (indicated fuel flow rate) that is a flow rate of the reforming raw material at which the oxygen ratio λ of the mixed gas becomes the determination oxygen ratio λa is calculated (step S23 in FIG. 5). Then, the control device 15 (oxygen ratio changing unit) controls the raw material pump 11a5 so that the flow rate of the reforming raw material supplied by the raw material pump 11a5 becomes the indicated raw material flow rate Fa (step S24 in FIG. 5). Thereby, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 can be accurately and reliably set to the determination oxygen ratio λa. For this reason, incomplete combustion can be reliably generated in the combustion unit 36, and combustible components that have not been burned in the combustion unit 36 can be more reliably introduced into the combustion catalyst 28. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst 28.

  The control device 15 (instructed fuel flow rate calculation unit) calculates the indicated raw material flow rate Fa based on the temperature T1 of the reforming unit 33 detected by the reforming unit temperature sensor 33a (reforming unit temperature detection unit) (FIG. 5 step S23). That is, the control device 15 (instructed fuel flow rate calculation unit) calculates the composition of the reformed gas generated by the reforming unit 33 based on the temperature T1 of the reforming unit 33 (see FIGS. 2 and 5). Step S12). Then, the control device 15 (indicated fuel flow rate calculation unit) calculates the indicated raw material flow rate Fa based on the calculated reformed gas composition. As a result, the indicated raw material flow rate Fa is calculated with higher accuracy than the case where it is not based on the composition of the reformed gas so that the oxygen ratio λ of the mixed gas introduced into the combustion section 36 becomes the determination oxygen ratio λa. For this reason, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 can be made the determination oxygen ratio λa.

  In this way, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 is accurately and reliably set to the determination oxygen ratio λa. Thereby, generation | occurrence | production of the soot in the combustion part 36 resulting from the oxygen ratio (lambda) reducing too much (for example, less than 1) is prevented.

  In the present embodiment, the control device 15 (determination unit) determines that the single temperature sensor 28b (temperature detection unit) when the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is changed to the determination oxygen ratio λa. When the second specified time TMb has elapsed after the time during which the exhaust gas temperature T2 detected by step S2 does not reach the determination temperature T2a (YES in step S26 of FIG. 5), the catalytic reaction of the combustion catalyst 28 decreases. (Step S42). In this way, it is possible to determine a decrease in the catalytic reaction of the combustion catalyst 28 without providing a plurality of temperature sensors 28b. For this reason, the increase in the manufacturing cost of a fuel cell system can be suppressed.

(Second catalytic reaction decrease judgment process)
Hereinafter, with reference to the flowchart shown in FIG. 6, the “second catalyst reaction decrease determination process” will be described with respect to differences from the “first catalyst reaction decrease determination process”. For each process of the “second catalyst reaction decrease determination process”, the same process number as the “first catalyst reaction decrease determination process” is assigned the same step number as the “first catalyst reaction decrease determination process”. The description is omitted. In the “second catalytic reaction decrease determination process”, the fuel cell is maintained while maintaining the flow rate of the reforming raw material supplied to the evaporation section 32, that is, while maintaining the flow rate of the reformed gas supplied to the fuel cell 34. By reducing the sweep current swept from 34 and the flow rate of the cathode air supplied to the fuel cell 34, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 is made the determination oxygen ratio λa, and the combustion catalyst 28. This is a method for determining whether or not the catalytic reaction is reduced.

  Instead of step S12, step S212 is executed. In step S212, the control device 15 (indicated current calculation unit, indicated oxidant gas flow rate calculation unit) is based on the flow rate of the reforming material supplied to the evaporation unit 32 detected by the reforming material flow rate sensor 11a3. Then, calculation of the flow rate of the reformed gas supplied from the reforming unit 33 to the fuel cell 34 is started (1 in FIG. 3). Further, the control device 15 (indicated current calculation unit, indicated oxidant gas flow rate calculation unit) starts calculating the composition of the reformed gas supplied from the reforming unit 33 to the fuel cell 34 by the same method as in step S12. (2 in FIG. 3). Next, the control device 15 (indicated current calculation unit, indicated oxidant gas flow rate calculation unit) determines the flow rate of the reformed gas supplied to the fuel cell 34 and the reforming by the above-described method described with reference to FIG. Based on the gas composition, calculation of the flow rate of each combustible component of the reformed gas supplied to the fuel cell 34 is started (3 in FIG. 3). When step S212 ends, the control device 15 advances the program to step S21.

  Instead of step S23, step S223 is executed. In step S223, the control device 15 (indicated current calculation unit, indicated oxidant gas flow rate calculation unit) calculates each combustible component of the reformed gas calculated in step S212 by the method described above with reference to FIG. Based on the flow rate, the command current Ia and the command cathode air flow rate Fb, which are the sweep currents swept from the fuel cell 34, which are the determination oxygen ratio λa, are calculated. If the sweep current is set to the instruction current Ia lower than the current sweep current value, the flow rate of hydrogen and the flow rate of oxygen consumed in the fuel cell 34 are reduced. If the flow rate of cathode air corresponding to the decrease in the flow rate of oxygen consumed in the fuel cell 34 is reduced while the flow rate of the reformed gas supplied to the fuel cell 34 is maintained, the fuel cell 34 Only the flow rate of the hydrogen consumed in the fuel gas decreases, the flow rate of hydrogen contained in the mixed gas supplied to the combustion unit 36 increases, and the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 decreases. Using such a method, the control device 15 calculates the command current Ia and the command cathode air flow rate Fb. When step S223 ends, the control device 15 advances the program to step S224.

  In step S224, the control device 15 (oxygen ratio changing unit) gradually changes the sweep current from the fuel cell 34 to the command current Ia calculated in step S223 over a predetermined time (for example, several seconds to several tens of seconds). As a result, the inverter device 13 is controlled. At the same time, the control device 15 (oxygen ratio changing unit) determines the flow rate of the cathode air supplied to the fuel cell 34 based on the flow rate of the cathode air detected by the cathode air flow rate sensor 11c2 for a predetermined time (for example, The cathode air blower 11c1 is feedback-controlled so that the instruction cathode air flow rate Fb calculated in step S223 is gradually changed over several seconds to several tens of seconds). In this way, by gradually changing the flow rates of the sweep current and the cathode air, the occurrence of partial blow-off in the combustion portion 36 due to a sudden change in the flow rate of the mixed gas supplied to the combustion portion 36 and the combustible component, The occurrence of complete blowout is prevented. By the processing in step S224, the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 gradually becomes the determination oxygen ratio λa. When step S224 ends, the control device 15 advances the program to step S25.

  In this way, the control device 15 (oxygen ratio changing unit) causes the inverter device 13 to reduce the sweep current compared to before the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 is set to the determination oxygen ratio λa. The cathode air blower 11c1 (oxidant gas supply unit) is controlled so that the flow rate of the cathode air decreases by the amount of cathode air (oxidant gas) corresponding to the decrease in the sweep current. By controlling, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 is set to the determination oxygen ratio λa (step S224 in FIG. 6).

  As a result, the flow rate of hydrogen consumed in the fuel cell 34 is reduced due to a decrease in the sweep current, and accordingly, the flow rate of hydrogen introduced into the combustion unit 36 is increased. Further, although the flow rate of oxygen consumed by the fuel cell 34 is reduced due to the decrease in the sweep current, the flow rate of the cathode air is reduced by the amount corresponding to the flow rate of the cathode air corresponding to the decrease in the sweep current, so that the combustion unit The flow rate of oxygen supplied to 36 does not increase. As a result, the flow rate of oxygen supplied to the combustion unit 36 is not increased, the flow rate of combustible components supplied to the combustion unit 36 can be reliably increased, and the oxygen ratio of the gas introduced into the combustion unit 36 can be increased. The determination oxygen ratio λa can be obtained. For this reason, incomplete combustion can be generated in the combustion part 36, and the combustible component which was not burned in the combustion part 36 can be reliably introduced into the combustion catalyst 28. Therefore, it is possible to reliably determine a decrease in the catalytic reaction of the combustion catalyst 28.

  In this way, whether or not the oxygen ratio of the gas introduced into the combustion section 36 is set to the determination oxygen ratio λa without increasing the flow rate of the reforming raw material, and the decrease in the catalytic reaction of the combustion catalyst 28 is reduced. Is determined. Thereby, overheating of the fuel cell module 11 due to an increase in the flow rate of the reforming raw material is prevented.

  Based on the flow rate of the reforming raw material supplied from the raw material pump 11a5, the control device 15 (indicated current calculation unit) is a fuel cell 34 in which the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 becomes the determination oxygen ratio λa. The command current Ia which is a current swept from is calculated (step S223 in FIG. 6). Then, the control device 15 (instructed oxidant gas flow rate calculation unit) determines the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 based on the flow rate of the cathode air supplied by the raw material pump 11a5 and the calculated indicated current Ia. An instruction cathode air flow rate Fb (indicating oxidant gas flow rate) which is a cathode air flow rate at which the determination oxygen ratio λa is obtained is calculated (step S223 in FIG. 6). The control device 15 (oxygen ratio changing unit) controls the inverter device 13 so that the sweep current swept from the fuel cell 34 becomes the command current Ia, and the flow rate of the cathode air supplied to the fuel cell 34 is The raw material pump 11a5 is controlled so as to be the indicated cathode air flow rate Fb (step S224 in FIG. 6).

  Thus, the command current Ia at which the oxygen ratio λ of the mixed gas becomes the determination oxygen ratio λa is calculated, the sweep current swept from the fuel cell 34 is changed to the command current Ia, and the oxygen ratio λ of the mixed gas is determined. The command cathode air flow rate Fb having an oxygen ratio λa is calculated, and the cathode air flow rate supplied by the raw material pump 11a5 is changed to the command cathode air flow rate Fb. Thereby, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 can be accurately and reliably set to the determination oxygen ratio λa. For this reason, incomplete combustion can be reliably generated in the combustion unit 36, and combustible components that have not been burned in the combustion unit 36 can be more reliably introduced into the combustion catalyst 28. Therefore, it is possible to more reliably determine the decrease in the catalytic reaction of the combustion catalyst 28.

  In addition, the control device 15 (indicated current calculation unit) calculates the instruction current Ia based on the temperature T1 of the reforming unit 33 detected by the reforming unit temperature sensor 33a (reforming unit temperature detection unit). That is, the control device 15 (indicated fuel flow rate calculation unit) calculates the composition of the reformed gas generated by the reforming unit 33 based on the temperature T1 of the reforming unit 33 (see FIGS. 2 and 6). Step S212). Then, the control device 15 (indicated fuel flow rate calculation unit) calculates the instruction current Ia based on the calculated reformed gas composition. As a result, the indicated raw material flow rate Fa is calculated with higher accuracy than the case where it is not based on the composition of the reformed gas so that the oxygen ratio λ of the mixed gas introduced into the combustion section 36 becomes the determination oxygen ratio λa. For this reason, the oxygen ratio λ of the mixed gas supplied to the combustion unit 36 can be more reliably set to the determination oxygen ratio λa.

(Another embodiment)
In the embodiment described above, the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to the determination oxygen ratio λa lower than the incomplete combustion start oxygen ratio λ0, and the anode off gas is incompletely combusted in the combustion unit 36. The flow rate of the combustible component contained in the combustion gas introduced into the combustion catalyst 28 from the combustion unit 36 is increased to determine whether the catalytic reaction of the combustion catalyst 28 is reduced. However, as shown in FIG. 2, the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to a second determination oxygen ratio λa2 that is higher than the oxygen ratio λ (for example, 1.6) during normal operation, Even if it is embodiment which determines whether the catalytic reaction of the combustion catalyst 28 is falling, it does not interfere.

  When the oxygen ratio λ of the mixed gas introduced into the combustion unit 36 is set to the second determination oxygen ratio λa2 or more, the flow rate of the combustible component contained in the anode off-gas is too small relative to the flow rate of oxygen (fuel). (Lean state), combustion in the combustion section 36 is partially or completely stopped. Then, the ratio of the combustible component contained in the combustion gas introduced into the combustion catalyst 28 increases dramatically. If the catalytic reaction of the combustion catalyst 28 has not decreased, the combustible component is burned by the combustion catalyst 28. Then, as shown by the solid line in FIG. 2, the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 rises to the second determination temperature T2b (shown by 2 in FIG. 2), and the catalytic reaction of the combustion catalyst 28 is reduced. It is determined that there is no. On the other hand, when the catalytic reaction of the combustion catalyst 28 is lowered, the combustible component is not completely burned by the combustion catalyst 28. For this reason, as shown by the broken line in FIG. 2, the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 hardly rises and becomes lower than the second determination temperature T2b, and the catalytic reaction of the combustion catalyst 28 decreases. It is determined that

  In the embodiment described above, the temperature sensor 28b (temperature detection unit) detects the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28. However, the temperature sensor 28b (temperature detection unit) may be an embodiment that detects the temperature of the combustion catalyst 28. In the case of this embodiment, the control device 15 (determination unit) determines whether or not the catalytic reaction of the combustion catalyst 28 has decreased based on the temperature of the combustion catalyst 28 detected by the temperature sensor 28b.

  In the embodiment described above, the composition of the reformed gas is calculated based on the temperature T1 of the reforming unit 33 detected by the reforming unit temperature sensor 33a (the reforming unit temperature detecting unit). However, a temperature sensor (reformer temperature detector) for detecting the temperature of the reformed gas flowing out from the reformer 33 is provided, and the reformed gas is based on the temperature of the reformed gas detected by this temperature sensor. However, there is no problem even if the composition is calculated.

  There may be an embodiment in which the process for determining whether or not the catalytic reaction in the combustion catalyst 28 is reduced is started after the power generation amount (sweep current value) in the combustion battery 34 is reduced. In the case of this embodiment, even if the combustion catalyst 28 is deteriorated and the combustible component is not completely burned by the combustion catalyst 28, the amount of the combustible component discharged from the combustion catalyst 28 to the outside. Can be reduced.

(Fuel cell system of the second embodiment)
Below, the fuel cell system 200 of 2nd embodiment is demonstrated using FIG. 7 about the difference from the fuel cell system 100 of embodiment described above (1st embodiment). In the fuel cell system 200 of the second embodiment, in addition to the temperature sensor 28b (first temperature detection unit) that detects the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28, it is introduced from the combustion unit 36 into the combustion catalyst 28. A second temperature sensor 28c (second temperature detection unit) for detecting the temperature T3 of the combustion gas is provided.

  In step S25 of FIGS. 5 and 6, the control device 15 (determination unit) detects the combustion detected by the second temperature sensor 28c from the temperature T2 of the exhaust gas exhausted from the combustion catalyst 28 detected by the temperature sensor 28b. A temperature difference ΔT obtained by subtracting the temperature T3 of the combustion catalyst introduced into the catalyst 28 is calculated. Then, when the control device 15 (determination unit) determines that the temperature difference ΔT is less than the specified temperature difference ΔTa (step S25: YES), the program proceeds to S41. On the other hand, if the control device 15 (determination unit) determines that the temperature difference ΔT is less than the specified temperature difference ΔTa (step S25: NO), the program proceeds to S31.

  In the second embodiment, an increase in the temperature of the combustion catalyst 28 with an increase in the flow rate of the combustible component introduced into the combustion catalyst 28 is reliably detected regardless of the temperature of the combustion gas introduced into the combustion catalyst. can do. For this reason, it can be determined with higher accuracy whether the catalytic reaction of the combustion catalyst 28 is reduced.

  11a5 ... Raw material pump (fuel supply unit), 11c1 ... Cathode air blower (oxidant gas supply unit), 13 ... Inverter device (sweep current changing unit), 15 ... Control device (oxygen ratio changing unit, determining unit, indicated fuel flow rate) Calculation unit, command current calculation unit, command oxidant gas flow rate calculation unit), 28 ... combustion catalyst, 28b ... temperature sensor (temperature detection unit, first temperature detection unit), 28c ... second temperature sensor (temperature detection unit, first Two temperature detectors), 33 ... reforming unit, 33a ... reforming unit temperature sensor (reforming unit temperature detection unit), 34 ... fuel cell, 36 ... combustion unit, 100 ... fuel cell system (first embodiment), 200 ... Fuel cell system (second embodiment)

Claims (10)

A reforming section for generating fuel from the reforming water and the reforming raw material;
A fuel supply unit for supplying the reforming raw material to the reforming unit;
A fuel cell that generates electric power from the fuel and oxidant gas generated by the reforming unit;
A combustion section for burning an anode off-gas containing combustible components exhausted from the fuel cell with an oxidant gas;
A combustion catalyst containing the unburned combustible component exhausted from the combustion section, and burning the combustible component contained in the combustion gas by a catalytic reaction;
A temperature detector for detecting a temperature related to the combustion catalyst;
The oxygen ratio is changed by changing the oxygen ratio obtained by dividing the oxygen flow rate introduced into the combustion unit by the ideal oxygen flow rate necessary for completely burning the combustible component introduced into the fuel unit. An oxygen ratio changing unit that increases the flow rate of the unburned combustible component introduced from the combustion unit to the combustion catalyst,
When the oxygen ratio is changed by the oxygen ratio changing unit, it is determined whether or not the catalytic reaction of the combustion catalyst is lowered based on the temperature related to the combustion catalyst detected by the temperature detecting unit. A fuel cell system.   2. The fuel cell according to claim 1, wherein the oxygen ratio changing unit lowers the oxygen ratio to a determination constant oxygen ratio lower than an incomplete combustion starting oxygen ratio at which incomplete combustion of the combustible component occurs in the combustion unit. system.   The oxygen ratio changing unit increases the flow rate of the fuel supplied by the fuel supply unit to reduce the oxygen ratio to the determined constant oxygen ratio compared to before reducing the oxygen ratio to the determined constant oxygen ratio. The fuel cell system according to claim 2, which is reduced. A sweep current changing unit for changing a sweep current which is a current swept from the fuel cell;
An oxidant gas supply unit for supplying the oxidant gas to the fuel cell,
The oxygen ratio changing unit controls the sweep current changing unit so that the sweep current is reduced as compared to before the oxygen ratio is decreased to the determined constant oxygen ratio, and the oxygen ratio changing unit is configured to respond to the decrease in the sweep current. 3. The fuel cell system according to claim 2, wherein the oxygen ratio is reduced to the determined constant oxygen ratio by controlling the oxidant gas supply unit so that the flow rate of the oxidant gas is reduced by an amount of the oxidant gas. . An indication of the flow rate of the fuel at which the oxygen ratio is reduced to the determined constant oxygen ratio based on a sweep current that is a current swept from the fuel cell and a flow rate of the oxidant gas supplied to the fuel cell. An instruction fuel flow rate calculation unit for calculating the fuel flow rate,
The fuel cell system according to claim 3, wherein the oxygen ratio changing unit controls the fuel supply unit so that a flow rate of the fuel supplied by the fuel supply unit becomes the indicated fuel flow rate. Based on the flow rate of the fuel supplied by the fuel supply unit, an instruction current calculation unit that calculates an instruction current that is a current swept from the fuel cell in which the oxygen ratio is reduced to the determined constant oxygen ratio;
Based on the flow rate of the fuel supplied by the fuel supply unit and the command current calculated by the command current calculation unit, the directed oxidation is a flow rate of the oxidant gas at which the oxygen ratio is reduced to the determined constant oxygen ratio An instruction oxidant gas flow rate calculation unit for calculating the agent gas flow rate,
The oxygen ratio changing unit controls the sweep current changing unit so that the sweep current swept from the fuel cell becomes the command current, and the flow rate of the oxidant gas supplied to the fuel cell is The fuel cell system according to claim 4, wherein the oxidant gas supply unit is controlled to achieve an indicated oxidant gas flow rate. A reforming unit temperature detecting unit for detecting the temperature of the reforming unit;
The fuel cell system according to claim 5, wherein the command fuel flow rate calculation unit calculates the command fuel flow rate based on the temperature of the reforming unit detected by the reforming unit temperature detection unit. A reforming unit temperature detecting unit for detecting the temperature of the reforming unit;
The fuel cell system according to claim 6, wherein the command current calculation unit calculates the command current based on the temperature of the reforming unit detected by the reforming unit temperature detection unit. The temperature detection unit detects the temperature of exhaust gas exhausted from the combustion catalyst or the temperature of the combustion catalyst,
When the oxygen ratio is changed by the oxygen ratio changing unit, and the temperature detected by the temperature detecting unit is lower than the determination temperature, the determining unit has a reduced catalytic reaction of the combustion catalyst. The fuel cell system according to any one of claims 1 to 8, wherein the fuel cell system is determined. The temperature detector is
A first temperature detector for detecting the temperature of exhaust gas exhausted from the combustion catalyst or the temperature of the combustion catalyst;
A second temperature detector for detecting the temperature of the combustion gas introduced into the combustion catalyst;
Consisting of
The determination unit is a temperature difference obtained by subtracting the temperature detected by the second temperature detection unit from the temperature detected by the first temperature detection unit when the oxygen ratio is changed by the oxygen ratio change unit. The fuel cell system according to any one of claims 1 to 8, wherein when the temperature difference is less than a specified temperature difference, it is determined that the catalytic reaction of the combustion catalyst is reduced.

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